CATALOGUE OF GEMS AND PRECIOUS STONES. 11 



LIST OF SPECIMENS. 

 BRAZIL. 



Step brilliant, rectangular girdle; brown-green; 1.39 carat?; 11 by (l by 



3 mm No. 568 



Brilliant, rectangular girdle; dark green; 1.03 carats; 7 by 6 by 4 mm No. 566 



Step, rectangular girdle; brown-green; 0.83 carat; 10 by 4.5 by 2 mm Xo. 569 



Step brilliant, square girdle; brown-green; 0.72 carat; 6 by 3.5 mm No. 567 



Aquamarine. — See under Beryl. 



Aragonite. — See under Calcite and Aragonite. 



AXINITE. 



Composition. — Iron calcium aluminum hydrous boro-silicate, 

 FeCa 2 Al 2 (OH)(BSi 4 15 ). 



Crystallization . — Triclinic; habit wedge-shaped. 



Color. — Brown; sometimes violet, violet-brown, or yellow-brown; 

 essential, due to the iron, and to manganese which may replace it; 

 strongly pleochroic, green to brown to blue. 



Luster. — Brilliant-vitreous ; transparent. 



Hardness. — 6.5; a fairly durable stone. 



Specific gravity. — 3.30 ± 0.05. 



Optical properties. — Mean refractive index 1.68; double refraction 

 weak, 0.009; optically biaxial, negative. 



Axinite may be distinguished from tourmaline and other similar 

 minerals by its pleochroism, specific gravity, and optical properties. 

 It occurs in veins, chiefly in metamorphic rocks and is in little de- 

 mand as a precious stone, because of unattractive colors and brittJo- 

 ness. Value purely arbitrary. 



LIST OF SPECIMENS. 



FRANCE (DAUPHINE). 



Step-brilliant, square girdle; violet-brown; 1.59 carats; 7.5 by -1.5 mm.... No. 581 



AZURITE. 



Composition. — Hydrous copper carbonate, Cu 3 (OH) 2 (CO) 2 . 



Crystallization . — Monoclinic . 



Color. — Dark blue, characteristic of many compounds of copper. 



Luster. — Vitreous; translucent to opaque. 



Hardness. — 4; too soft for extensive use as a precious stone. 



Specific gravity. — 3. 80 ±0.05. 



Optical properties. — Mean refractive index 1.9; double refract ion 

 very strong, 0.20; biaxial, positive. 



The mineral dissolves readily in hydrochloric acid with efferves- 

 cence to a yellow solution. It may as a rule be distinguished from 

 other blue precious stones by its intense color, softness, and solu- 



